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Large Lyman-alpha opacity fluctuations and low CMB tau in models of late reionization with large islands of neutral hydrogen extending to z<5.5

4 Pith papers cite this work. Polarity classification is still indexing.

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abstract

High-redshift QSO spectra show large spatial fluctuations in the Ly-alpha opacity of the intergalactic medium on surprisingly large scales at z>~5.5. We present a radiative transfer simulation of cosmic reionization driven by galaxies that reproduces this large scatter and the rapid evolution of the Ly-alpha opacity distribution at 5<z<6. The simulation also reproduces the low Thomson scattering optical depth reported by the latest CMB measurement and is consistent with the observed short near-zones and strong red damping wings in the highest-redshift QSOs. It also matches the rapid disappearance of observed Ly-alpha emission by galaxies at z>~6. Reionization is complete at z=5.3 in our model, and 50% of the volume of the Universe is ionized at z=7. Agreement with the Ly-alpha forest data in such a late reionization model requires a rapid evolution of the ionizing emissivity of galaxies that peaks at z~6.8. The late end of reionization results in a large scatter in the photoionisation rate and the neutral hydrogen fraction at redshifts as low as z<~5.5 with large residual neutral 'islands' that can produce very long Gunn-Peterson troughs resembling those seen in the data.

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The Lumina Project: Intergalactic Clumping and Recombination Sinks

astro-ph.GA · 2026-06-16 · unverdicted · novelty 4.0

Simulations show recombination-weighted clumping is systematically lower than density-based measures, density-only prescriptions overpredict rates by 1.29-1.84 depending on redshift, and a new phase-space clumping factor isolates thermal and ionization effects at fixed density.

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